The conjugate acid of is
a. H2PO4
b· H4PO4
c· H3PO4
d· HPO42
e· OH
The Correct Answer and Explanation is :
The correct answer is b. H4PO4.
Explanation:
A conjugate acid is formed when a base accepts a proton (H⁺). In the case of phosphate species, they exhibit different protonation states depending on the pH of the solution. To identify the conjugate acid of a given species, we must understand how these species can accept protons.
- H₂PO₄⁻ (dihydrogen phosphate): This is the species in the middle of the phosphate ion’s dissociation. If H₂PO₄⁻ accepts a proton (H⁺), it forms H₃PO₄ (phosphoric acid). This makes H₂PO₄⁻ the conjugate base of H₃PO₄. It is not the conjugate acid.
- H₄PO₄ (tetrahydrogen phosphate): When a phosphate ion accepts a proton (H⁺), the resulting species is H₄PO₄. This is the correct conjugate acid for the phosphate base species. The protonation of H₃PO₄ results in H₄PO₄, which is a less common form of phosphate but still a conjugate acid.
- H₃PO₄ (phosphoric acid): This is already an acid, not a base. It can lose protons, but it cannot accept one to form a conjugate acid. It is a weak acid that dissociates to form H₂PO₄⁻.
- HPO₄²⁻ (hydrogen phosphate): This is the conjugate base of H₂PO₄⁻. If it accepts a proton, it forms H₂PO₄⁻, not H₄PO₄.
- OH⁻ (hydroxide): Hydroxide is a strong base, not related to phosphate ions. If OH⁻ accepts a proton, it forms H₂O (water), but it is not connected to phosphate species in this context.
Thus, H₄PO₄ is the conjugate acid of H₃PO₄, and it is formed when H₃PO₄ accepts a proton.